1) Single is better compatibility and efficiency. Although SLI is better at times when a card better is way more expensive, like 2 780 and a Titan Z, 2 760 does not get better than 1 970. Plus, assume SLI is 2/3 the performance 2 of the cards. The 2 760 will be, in PassMark, 6765, estimated, while the 970 scores 8701.
2) The only thing he hasn't said was what setting he's running on.